This invention relates to hydronic heating systems for dwellings, offices, etc. and more particularly to systems having one or more satellite distribution stations feeding several kinds of heating loops requiring different temperature water and so providing multi-temperature heating loop operation.
Hydronic heating systems for heating the rooms in a dwelling, office, etc, are used widely in Europe and to a lesser extent in the United States. Water heated in a boiler is distributed to heating loops of tubing in the dwelling that carry the heat by radiation, conduction and convection to the rooms in the dwelling. A common technique provides a boiler hot water supply feeding the supply header of the distribution station for the heating loops and the boiler water return to which the station return header of the heating loops connects. The return water is heated in the boiler and sent out again to the station as hot supply water, and so the water is cycled through the essentially closed system. One or more water pumps in this system keep the water flowing and valves control water flow rates through the loops depending on demand.
A heating loop may include several heating elements like baseboard finned tubing or wall mounted radiators that are the principal heat exchangers of the loop, or the tubing itself may be the principal heat exchanger of the loop. In the latter case the tubing is usually buried in the floor of a room and the tubing heats the floor. Often the tubing is buried in a special concrete and so heat exchange is principally by conduction and radiation to the concrete, which in turn heats the room by some conduction and convection, but principally by radiation. Hence, this type of heating is called Radiant Floor Heating (RFH). Similarly, when the tubing is buried in the wall, the heating is called Radiant Wall Heating (RWH).
In such RFH and RWH systems and other hydronic heating systems using baseboard finned tubing elements or wall mounted radiators, the supply water temperature from the boiler must be controlled so that it does not exceed certain limits that are substantially lower than the usual boiler supply water temperature. There are several reasons for this: first, the temperature of radiator elements on the wall must not be so high that they are not safe to touch; second, for RFH the floor temperature must not be uncomfortable hot; and third, where the tubing is plastic, the water temperature for some plastic materials must not exceed about 140.degree. F.
In hydronic heating systems subject to such water temperature limitations, where the boiler is powered by burning fossil fuels, the boiler water supply temperature is usually well above 140.degree. F. and often at about 180.degree. F. to 200.degree. F., and so the boiler supply temperature must be stepped down before it is fed to the heating loops.
In the past, it has been the practice to mix relatively cooler boiler return water with the hot boiler supply water to "dilute" the temperature of the supply water fed to the heating loops. An electrically controlled motorized three-way mixing valve has been used in the boiler supply line that feeds the supply header for the heating loops, between the boiler supply and the heating loops supply header. The mixing valve has two inputs and one output. One input is directly from the boiler hot water supply, the other input is from the return header of the heating loops and the output is directly to the supply header of the heating loops. The mixing valve motor is electrically energized by remote reset controls that sometimes respond to outside ambient temperature, inside room temperature, boiler water temperature, supply header water temperature, etc.
In an effort to reduce expense, non-motorized three-way valves have been used in the boiler supply line. Systems using non-motorized three-way valves with supply header water temperature feedback are described in my U.S. Pat. No. 5,119,988, which issued Jun. 9, 1992, entitled: "Hydronic Heating Water Temperature Control System". That patent describes several hydronic heating systems with a non-motorized (non-electric) three-way valve having supply water temperature feedback to the valve controller. In some of those systems, the valve is a three-way diverting valve in the boiler return water line and in another system, it is a three-way mixing valve in the boiler supply water line. The diverting valve and the mixing valve are quite different. The diverting valve has one input and two outputs and diverts water from the return line (on the way from the heating loop return header to the boiler return), to the boiler supply line that feeds the loop supply header, diluting the supply water (reducing its temperature) that is fed to the heating loop supply header.
That patent also teaches use of a non-electric thermostatic actuator head attached to the valve for positioning the valve stem and controlled by a capillary temperature sensor. Thus, the valve is modulated by non-electric feedback of the diluted supply water temperature. The bulb of the capillary sensor is inserted into the diluted supply water or it may be clamped to the supply line next to the supply header so that it is at the temperature of water in the supply header. Capillary fluid in the bulb expands with temperature applying a pressure force through the capillary to the actuator head and so the valve is modulated to increase or decrease the flow of return water through the valve as necessary to maintain the temperature of the heating loop supply header water at or below a predetermined value. That value can be set by a mechanical setting on the actuator head and so an accurate reading of the supply header water temperature is made continuously and simultaneously any deviation from the setting is immediately nulled by modulating the valve.
Techniques for controlling heater loop supply header water temperature, depending on outdoor ambient temperature are described in my co-pending U.S. patent application Ser. No. 222,884, filed Apr. 5, 1994, entitled: "Hydronic Heating Outdoor Temperature Reset Supply Water Temperature Control System". That application describes systems using a modulated three-way valve that can be a diverting valve in the boiler return line or a mixing valve in the boiler supply line, wherein feedback to the valve is from the diluted supply water temperature and is derived from a sensor bulb immersed in the diluted supply water or clamped to the supply line next to the heating loop supply header so that it is at the temperature of the diluted supply water and that feedback is modified by outdoor ambient temperature that is derived from another sensor bulb exposed to outdoor air temperature. Fluid from both bulbs is connected by capillary tubes from the bulbs to the diverting valve actuator head which drives (pushes) the valve stem into the valve against the valve spring, or releases the valve stem so that the valve spring pushes it out and so the valve is modulated to increase or decrease the dilution of supply water, as necessary to maintain the diluted supply water temperature at a predetermined value depending on outdoor ambient temperature.
Embodiments described in said co-pending U.S. application Ser. No. 222,884 that use a mixing valve in the supply line show two different orientations and with different thermostatic actuator heads. The usual configuration of such a mixing valve is with the first input in line with the output and the second input at a right angle thereto. The usual orientation of such a mixing valve in the supply line of the hydronic heating system is with the first input from the boiler supply line, the second input from the return line and the output is to the heating loop supply header. In the new orientation of the mixing valve in the supply line, the inputs are reversed so that a conventional push/release type actuator head can be used on the valve to carry out the required performance.
RFH and RWH systems using embedded plastic tubing and other hydronic heating systems using wall radiators and/or baseboard finned tubing elements are some of the different kinds oh heating loops. Clearly, the temperature limitation of a heating loop depends first on how and where the loop is installed, creature comfort and the materials in the loop. As the term "kind" of loop is used herein, it means the temperature requirements and limitations of the loop and so loops of the same kind have the same temperature requirements and limitations. For example: the temperature of baseboard finned tubing radiator elements can be quite high, because they are metal tubes, can be shielded and are not usually touched, even accidentally, whereas wall radiators are not shielded and must not be too hot to touch; for RFH where the tubing is beneath the floor boards, the tubing can be hotter than where the tubing is on top of the floor boards; for RWH the tubing is covered by only thin gypsum board and so must be well below 100.degree. F.; and even the best cross-linked plastic tubing should not be exposed to water above 140.degree. F.
Where the hydronic system is used for ice and snow melting, thermal shock of the outdoor surface that is heated can occur even when there is a heat exchanger between the main or "front end" distribution station (the boiler water system) and the outdoor (anti-freeze) water system. Thermal shock and techniques of dealing with it are described in my co-pending U.S. patent application Ser. No. 275,492, filed Jul. 15, 1994, entitled: "Hydronic Heating System With High And Low Temperature Shock Protection".
Since the temperature of boiler supply water fed to the main distribution station is usually well above 140.degree. F. and often at about 180.degree. F. to 200.degree. F., the boiler supply water temperature may be alright for some "kinds" of heating loops like baseboard finned copper tubing, but must be much lower for other "kinds" of heating loops like RWH. The present application describes techniques and systems that provide several echelons of temperature ranges of loop supply water to accommodate the requirements of different "kinds" of heating loops.